1. Field of the Invention
The invention relates to a paper feed device for feeding continuous stationery, provided with lateral perforations, into the transport elements of a transfer station of a printing device with latent character image generation;
2. Description of the Related Art
Printing devices with latent character image generation such as are represented, for example, by laser printers, printing devices operating with LED pins or magnetic printers, are generally known and have been used successfully.
In non-mechanical printers, a latent character image is generated, generally with the aid of a laser or with the aid of magnetic recording means, on a photo carrier drum or a magneto-sensitive drum, which latent character image is developed in a developing station by the application of toner and is then transferred in the subsequent transfer station onto a web-shaped recording medium in the form of continuous stationery, or paper, provided with lateral perforations. The image consisting of toner and held loosely on the continuous stationery is fixed with the aid of a fixing device and is then placed by an automatic paper stacker on a paper delivery surface.
Rapid printing devices with latent character image generation of this type are operated together with EDP (Electronic Data Processing) systems and are operated and serviced by the same operating personnel. For this reason, the printing devices must be designed in such a way that a virtually uninterrupted printing operation is guaranteed. For this reason, when a stack of paper has been used up, a new stack of paper must be able to be deposited very rapidly without substantial interruption time. For this reason, printing devices of this type must be of ergonomically optimum design; this preferably applies to the depositing and removal of the paper and to the servicing of the entire plant.
Due to the complicated construction of printing devices of this type and the complicated paper transport path resulting therefrom, in the known non-mechanical printing devices the depositing and removal of the paper are difficult and awkward when the printer starts up and during print interruptions. For this purpose, the transfer station is customarily swiveled away from the intermediate support, e.g. a photo carrier drum, and the paper is deposited in the printing device by hand.
In this case, the paper guidance in the region of the transfer station is particularly problematic, especially in the region of the transfer point. It must thus be ensured that the paper is guided tautly during the printing operation and without clearance around the transfer station. Flapping of the paper in the region of the transfer point leads to disturbances in the transfer operation and consequently to a deterioration of the lettering image, e.g. in the form of smeared print or the like.
Furthermore, the paper transport device must be designed at the transfer station in such a way that a synchronous run of the paper with the photo carrier drum is guaranteed.
For this reason, it is customary in electrophotographic printing devices (such as disclosed in German Patent 2,717,315) to construct the entire transfer station as a uniform component which can be swiveled on and away and to provide paper tractors with paper transport pegs recording medium transport device at the transfer station, which paper transport pegs engage in the lateral perforation of the continuous stationery. In this case, one pair of tractors is arranged both at the input side and at the output side of the transfer station.
Tractors of this type generally comprise a tractor belt with tractor flaps arranged above it which press the paper against the tractor belt. Whereas the paper tractors on the output side are generally easily accessible, operation of the input-side tractor flaps is difficult due to the design.
A further problem consists in the exact depositing of the continuous stationery provided with lateral perforations in the tractor belts, in which case it must be ensured that the continuous stationery is deposited accurately and without clearance on the tractor belts, specifically on the transport pegs. For this purpose, the continuous stationery must be guided tautly around the transfer station, which naturally poses difficulties.